1. Field of the Invention
The present invention relates to a memory. More particularly, the present invention relates to a memory structure with repairing function and a repairing method thereof.
2. Description of the Related Art
With rapid development in the electronic technology, information exchange has become a routine activity. Since information exchange relies heavily on media with a large storage capacity, fast-responding memories have become an indispensable storage media for all information systems. As the information flow continues to rise, the data transmission rate must also increase. Consequently, there is a constant need for an increase in the storage capacity of memory devices. In general, the yield of application specific integrated circuit (ASIC) is often affected by possible damages in the embedded memory. To increase the yield of the memory embedded ASIC and reduce the production cost, a memory with a repairing function has been developed. When a portion of the memory cells in a main memory is defective, the defective portion can be repaired using reserved memory.
In a conventional memory with repairing function, the locations of the defective bits are first recorded during a product trial period. Thereafter, a laser beam is applied to melt a fuse so that an entire row (or column) of backup memory can replace an entire row (or column) in the main memory containing faulty bits.
FIG. 1 is a block diagram of a conventional memory with repairing function. Aside from having a main memory circuit 110, the memory 100 also has a redundant memory circuit 120 for replacing an entire row or column of memory cells when some of the memory cells in a row or a column of the main memory circuit 110 are defective. Its method of operation is described in more details in the following.
First, the row (or column) address of the main memory circuit 110 containing the defective memory cells is recorded. Thereafter, a laser beam is applied to cut off the corresponding fuses inside a fuse box 130 so that the row (or column) address of the defective memory is recorded in the fuse box 130. To access this memory 100 with conventional repairing function, the access memory address A is compared with all the row (or column) addresses of the defective memory recorded in the fuse box 130 through a compare logic circuit. If the row (or column) address of the access memory is one of the row (or column) addresses of the defective memory, the compare logic circuit 140 outputs a repair signal R representing the row (or column) address of the defective memory to a routing logic circuit 150. Thereafter, the routing logic circuit 150 changes the access pathway from the defective main memory circuit 110 to a backup memory address in the redundant memory circuit 120 corresponding a the row (or column) address of the defective memory.
Obviously, the repairing function of the conventional memory 100 has the following disadvantages.
1. The compare logic circuit 140 changes the access pathway of the routing logic circuit 150 only after the compare logic circuit 140 has received the access memory address and compared with all the row (or column) addresses containing defective memory recorded in the fuse box 130. Hence, the access efficiency is very low.
2. Because the repair is achieved by replacing an entire row or column, the ratio of the redundant memory circuit 120 to main memory remains high despite of significant improvement in processing capability and reduction in defect density.
3. The memory 100 with repairing function designed according to ASIC principles normally adopts a full custom design rather than an independent and separate memory circuit module and backup memory module design. Hence, the development time is longer, the application is rather inflexible and the design cost is high.